Apparatus for removing micronized coal from steam

ABSTRACT

Micronized coal is removed from coal-bearing steam by spraying stabilized petroleum oil into the steam and directing the resultant stream at a separation surface on which a coal-oil slurry is deposited and collected. Apparatus includes conduits which direct the resultant stream downward into a housing and normal to a surface on which the slurry is deposited by impact forces. In additional apparatus disclosed, the resultant stream is directed from a horizontal conduit circumferentially along the interior wall of a horizontally disposed cylindrical chamber at the top of the chamber and the coal-oil slurry deposited on the wall by centrifugal force is collected in a trough situated below a longitudinal slot at the bottom of the chamber. In both types of apparatus, after separation of the slurry the velocity of the steam is reduced to settle out remaining oil droplets and is then discharged to the atmosphere.

This is a division, of application Ser. No. 966,204 filed Dec. 4, 1978now U.S. Pat. No. 4,227,892.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for removing micronizedcoal from steam used to pulverize coal by spraying petroleum oil into astream of the coal-bearing steam and separating the coal and oil fromthe steam in the form of a coal-oil slurry through the use of impact orcentrifugal forces.

2. Prior Art

It is becoming increasingly common to mix pulverized coal with oil foruse as an industrial fuel. The finely divided coal required can beproduced by fluid energy mills which utilize high pressure steam toreduce the size of the coal particles through high speed collision andrefraction. The discharge of the mill is fed to cyclones which separatethe pulverized coal from the steam for mixing with the oil in properproportion for the desired fuel mixture.

Unfortunately, however, steam exiting the cyclones is ladden with largequantities of micron and submicron sized coal particles. Recovery ofthis residual coal is important because the fine coal particles arehighly explosive, are valuable for increasing the yield of the processof making the coal-oil mixture and cannot be released into theatmosphere under existing pollution regulations. The conventionalcollectors for suspended particulates, such as scrubbers, baghouses,condensors and electrostatic precipitators, cannot remove the micronizedcoal particles from the steam effectively without danger of fires,explosions and water pollution.

SUMMARY OF THE INVENTION

According to the invention, micronized coal is removed from steam usedto pulverize coal by spraying droplets of petroleum oil into a stream ofthe coal-bearing steam. The resultant stream is directed onto aseparation surface to deposit a coal-oil slurry thereon and the coal-oilslurry is collected from the separation surface. The droplets of oilinduce nucleation and agglomeration of the coal particles and create anoil film for impingement of the coal particles.

Separation of the coal-oil slurry from the steam car be effected bydirecting the steam containing coal and oil at the separation surface atsubstantially a right angle thereto to effect separation by impactforces, by directing the steam at a curved separation surface at ashallow angle to effect separation by centrifugal force or by acombination of these forces.

The coal-oil slurry may be concentrated through recycling by sprayingthe collected coal-oil slurry back into the flow of steam, coal and oil.In this manner the concentration of coal to oil can be increased fromabout 3-5% by weight up to the concentration of a suitable fuel mixturesuch as 50% by weight.

Preferably, the petroleum oil is stabilized with heat prior to beingsprayed into the stream of coal bearing steam to drive off the volatileconstituents. This reduces pollution in the effluent steam and reducesthe danger of fire. It is also preferable to cool the stabilized oil toabout 200° F. prior to introduction into the stream of coal-bearingsteam. However, the temperature of the stream should be kept above about220° F. to preclude condensation of the steam and, if necessary,superheated steam may be introduced into the stream for this purpose. Insome circumstances, it may be necessary to spray water into the streamto maintain the temperature below 300° F. to reduce the possibility offire.

After the coal-oil slurry has been removed from the steam, the velocityof the steam is reduced below the settling velocity of the oil dropletsto remove any residual oil from the steam.

The invention also encompasses apparatus for carrying out the aboveprocess. Such apparatus includes means for guiding a continuous flow ofcoal-bearing steam, means for spraying droplets of oil into the flow,means disposed in the flow of coal and oil-bearing steam defining aseparation surface on which the flow is directed to deposit thereon acoal-oil slurry and means for collecting the coal-oil slurry.

In one embodiment, the coal-bearing steam is guided by a length ofsubstantially straight conduit into which the oil is sprayed. Theconduit directs the flow of coal, oil and steam onto a plate which isdisposed in spaced relation to the end of the conduit and substantiallynormal thereto, whereby the coal-oil slurry is separated from the steamby impact forces. Preferably, the conduit is directed downward into ahousing having a discharge opening for the steam near the top thereof.Baffles in the housing direct the rising steam around the downwarddirected conduit to help maintain the desired operating temperature andto reduce the velocity of the steam below the settling velocity of theoil to effect separation of oil droplets remaining in the steam afterimpingement on the separation surface. Demisters immediately before thedischarge opening remove water droplets from the steam before it isexhausted to the atmosphere. Means are provided for introducingadditional noncoal bearing steam into the conduit when needed tomaintain the pressure in the housing above atmospheric pressure whichprecludes the entrance of oxygen into the housing, thereby reducing thefire hazard.

In another embodiment of the apparatus, the stream of coal andoil-bearing steam is directed at a curved separation surface to depositthe coal-oil slurry on this surface by centrifugal force. Moreparticularly, the separation surface is provided by a tube forming ahorizontally disposed chamber. The flow of coal, oil and steam isdirected circumferentially along the interior wall of the cylindricalchamber from a point near the top of the cylinder, such that thecoal-oil slurry is deposited on the curved interior wall of the chamber.The slurry is collected in a trough disposed below a slot which extendslongitudinally along the cylindrical chamber at the lowest pointthereof. The steam escapes through the slot into a housing forming anexpansion chamber in which the velocity of the steam is reduced belowthe settling velocity of any oil droplets remaining in the steam. Asecond trough in the housing collects the additional oil extracted fromthe steam and a deflector guides the steam flow across the first troughand into the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic front elevation view of apparatus in accordancewith one embodiment of the invention; and

FIG. 2 is a schematic isometric view of apparatus in accordance withanother embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to one embodiment of the invention, a pair of conduits 1 and 3are directed vertically downward into a housing 5. While the apparatusillustrated utilizes two conduits, it is to be understood that thenumber of conduits is not critical and one or three or more suchconduits could be utilized dependent upon the volume of coal-bearingsteam to be treated. The two conduits 1 and 3 are interconnected abovethe housing 5 by a header 7 which equalizes the flow in the two conduitsand provides pressure relief through a safety valve 9.

Steam laddened with micronized coal from the cyclones of a coalpulverizer plant is fed downward into the conduits 1 and 3. Petroleumoil supplied by a line 11 is sprayed into the stream of coal-bearingsteam concurrent with the flow by nozzles 13 mounted inside the conduits1 and 3. The resultant streams of coal, oil and steam are directed atseparation surfaces formed by plates 15 mounted in spaced relation tothe lower ends 17 of the conduits 1 and 3 by adjustable brackets 19. Asthe streams of coal, oil and steam impinge upon the upper surfaces ofthe plates 15, a slurry of coal and oil is deposited thereon. Thiscoal-oil slurry drains off the plates 15 and is collected in a trough 21at the bottom of the housing 5. The spacing between the plates 15 andthe ends of the conduits 1 and 3 may be adjusted by the adjustablebrackets 19.

A portion of the coal-oil slurry which is collected in the trough 21 isrecirculated by pump 23 through a line 25 and sprayed back into thestreams of coal, oil and steam by a second set of nozzles 27 mounted inthe conduits 1 and 3. This recirculation increases the concentration ofcoal in the slurry. Another portion of the coal-oil slurry is drawn offthrough the valve 29. By appropriate proportioning of the flow of makeupoil injected by the nozzles 13 to the flow of recirculated coal-oilslurry injected by the nozzles 27, the concentration of coal in theslurry can be adjusted. A continuous flow of coal-oil slurry of theselected concentration of coal can then be withdrawn through the valve29 at the same rate that makeup oil is supplied on line 11.

After impingement upon the plates 15, the steam rises in the housing 5where its velocity is slowed to below the settling velocity of oildroplets by baffles 31. Thus, any remaining oil in the steam settles outand drains into the trough 21 where it mixes with the slurry. The steamthen passes through a demister 33 which removes water droplets from thevapor and is discharged to the atmosphere through exhaust port 35 nearthe top of the housing 5.

The makeup oil supplied to the nozzles 13 is stabilized by driving offwith heat the hydrocarbon constituents which would be volatile at thesteam processing temperature (220°-300° F.). Thus the oil is injectedinto a pressure vessel 37 with superheated steam at a temperature above300° F. and the light hydrocarbons thus separated from the oil areliquified in condensor 39 and collected for suitable disposition. Thestabilized oil is transferred by pump 41 through cooler 43 and line 11to the nozzles 13.

It is desirable in operating the apparatus shown in FIG. 1 to maintainthe presure in the housing 5 above ambient pressure to maintain anonoxidizing atmosphere in the housing and thus eliminate the likelihoodof fire or explosion. Under some circumstances, it may be necessary toadd additional noncoal bearing steam to the system, such as through theheader 7, in order to maintain these conditions. It may also benecessary to add such additional steam to maintain the temperature inthe housing above about 220° F. to prevent formation of condensation.

FIG. 2 illustrates additional apparatus suitable for practicing theinvention. In this embodiment, the horizontally disposed cylindricalchamber 45 of a tubular structure 47 is intersected tangentially at itshighest point by a pair of horizontally oriented rectangular conduits49. Steam containing micronized coal from the cyclones of a fluid millcoal pulverizing plant is injected into the conduits 49 where it ismixed with droplets of petroleum oil injected into the flow throughnozzles 51. The petroleum oil, which may be stabilized in the mannerdiscussed in connection with the apparatus disclosed in FIG. 1, issupplied to the nozzles 51 through line 53. The resultant coal-oil andsteam mixture is injected into the chamber 45 circumferentially alongthe interior wall 55. The change in direction of the stream produced asit is guided by the curved wall 55 generates a centrifugal force whichdeposits a coal-oil slurry on the wall 55. The slurry which is driven bythe flow of steam and by gravity, flows down the curved wall 55 anddrains at the lowermost point of the cylindrical chamber 45 into atrough 57 mounted below a longitudinal slot 59 in the tubular structure47. The steam passes through the slot 59 into an expansion chamber 61formed by a housing 63. The steam is directed downward in the chamber 61by a downwardly depending wall 65 of the trough 57. Once below thebottom of wall 65, the steam rises in an area of increasingcross-section and escapes into the atmosphere through discharge opening67. The velocity of the steam is slowed in the expansion chamber 61below the settling velocity of oil droplets so that any remaining oilsettles to the bottom of chamber 61 where it is collected in a secondtrough 69. A line 71 drains both troughs 57 and 69. A deflector 73mounted on the trough 57 in the slot 59 directs the steam over thetrough 57 and reduces turbulence as the steam passes into the expansionchamber 61. Again, the number of conduits 49 is not critical but isrelated to the volume of coal-bearing steam to be processed and thedimensions of the apparatus. Likewise, the coal-oil slurry drawn offthrough line 71 may be recirculated by additional nozzles in theconduits 49 to achieve a desired concentration of the slurry. If needed,water can be injected into the conduits 49 through line 75 to controlthe temperature of the process.

EXAMPLE

Using the apparatus disclosed in FIG. 1, 14,000 pounds per hour of steamcontaining 200 pounds per hour of micronized coal was processed byinjecting the coal-bearing steam into the conduits at a rate of 100 feetper second. A positive 15" of water pressure was maintained in thehousing 5 and steam containing 9 pounds per hour of coal was exhaustedthrough discharge opening 35 at a velocity of 10 feet per second.Without recirculation, the slurry collected in trough 21 contained 3-5%coal by weight. By recirculating the slurry through nozzles 27 at therate of 50 gallons per minute, the concentration of coal in the slurrywas raised to a maximum of about 50% by weight using 2 gallons perminute of makeup oil.

While the invention has been disclosed in what is conceived to bepractical and effective embodiments thereof, it is recognized thatdepartures may be made therefrom which are fully within the spirit ofthe invention. Accordingly, the invention is not to be limited to thedetails specifically disclosed, but is to be accorded to full scope ofthe appended claims, including any and all equivalents.

I claim:
 1. An apparatus for removing micronized coal from a flow ofcoal-bearing steam exhausted from a coal pulverizer comprising:a conduitwhich guides the flow of coal-bearing steam; means disposed in saidconduit for introducing droplets of petroleum oil into said flow ofcoal-bearing steam; a tube forming a horizontally disposed cylindricalchamber, said conduit being arranged to introduce said flow of coal andoil bearing steam circumferentially along the interior wall of thecylindrical chamber from a point near the highest point thereof, todeposit a coal oil slurry on said internal wall through centrifugalforce; a trough disposed below a slot extending longitudinal through thecylindrical chamber at substantially the lowest point of the interiorwall of the cylindrical chamber, for collecting the coal-oil slurrydeposited on said wall; and a housing into which the steam escapesthrough said slot, said housing forming an expansion chamber in whichthe velocity of the steam is reduced and additional coal-oil slurrysettles to the bottom of said housing, and a second trough at the bottomof the housing for collecting the additional coal oil slurry.
 2. Theapparatus of claim 1 including a deflector mounted above said firsttrough to deflect steam across said first trough and into said housing,said deflector and cylindrical chamber defining an elongated spacethrough which the coal-oil slurry deposited on the interior wall of thecylindrical chamber can run into the trough.
 3. The apparatus of claim 2wherein the housing forming the expansion chamber includes a first andsecond section, said first section extending downwardly and being ofconstant cross-section and said second section extending upwardly fromthe lower end of said first section and being of increasingcross-section with a discharge opening in the upper portion thereofthrough which the steam may exit the apparatus.
 4. The apparatus ofclaim 3 wherein a wall depends downwardly from the first trough, saidwall extending toward, yet terminating short of, the second trough andsaid wall being parallel with one side of said housing such that,together, said wall and said side define two sides of the expansionchamber's first section of constant cross-section.
 5. The apparatus ofclaim 4 wherein the wall divides the housing into the first and secondsections of the expansion chamber.
 6. An apparatus for removingmicronized coal from a flow of coal-bearing steam exhausted from a coalpulverizer comprising:means for guiding the continuous flow of saidcoal-bearing steam; means for spraying droplets of petroleum oil intosaid flow of coal-bearing steam disposed in said guiding means such thatsaid oil is carried along with said flow; a housing connected to saidguiding means, said housing having an interior curved wall section alongwhich said flow is introduced tangentially and is guided in an arcuatepath whereby said coal-oil slurry is deposited on said curved wallsection by centrifugal force; trough means disposed below a slotextending longitudinally along the housing at a lower portion of thecurved wall section for collecting the coal oil slurry that is depositedon said curved wall; and a housing into which the steam escapes throughsaid slot, said housing forming an expansion chamber having a first andsecond section, said first section extending downwardly and being ofconstant cross-section and said second section extending upwardly andbeing of increasing cross section with a discharge opening in the upperportion thereof and a second trough at the bottom of said expansionchamber such that as the velocity of the steam is reduced in theexpansion chamber, additional coal slurry is deposited in said secondtrough and the steam exits through said discharge opening.